fai-monitor: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/sbin/fai-monitor - from package: fai-server

You may install the required package with command apt-get install {package}

Error in other languages:
fai-monitor: bevel nie gevind nie
fai-monitor: comandă negăsită
fai-monitor: comando não encontrado
fai-monitor: commande introuvable
fai-monitor: command not found
fai-monitor: käsku ei ole
fai-monitor: không tìm thấy lệnh
fai-monitor: komanda nerasta
fai-monitor: Kommando nicht gefunden.
fai-monitor: kommandot finns inte
fai-monitor: komut yok
fai-monitor: nie znaleziono polecenia
fai-monitor: níor aimsíodh an t-ordú
fai-monitor: no se encontró la orden
fai-monitor: no s'ha trobat l'ordre
fai-monitor: opdracht niet gevonden
fai-monitor: parancs nem található
fai-monitor: perintah tidak ditemukan
fai-monitor: príkaz nenájdený
fai-monitor: příkaz nenalezen
fai-monitor: команда не найдена
fai-monitor: командата не е открита
fai-monitor: 命令找不到
fai-monitor: コマンドが見つかりません